This invention is directed to methods of making an article bearing a relief image by forming a mask image from a film, transferring the mask image to a photosensitive material, and exposing the photosensitive material to a curing radiation. Photosensitive elements comprising a laser-ablatable mask layer on the surface of a photosensitive element have been reported. Such elements may be made into articles bearing a relief image without the use of a digital image negative or other separate masking device. The photosensitive elements having an ablatable mask layer (or a so-called “integral mask”) can be imaged by first imagewise exposing the photosensitive element with laser radiation (generally from an infrared laser under computer control) to selectively remove the mask layer in the exposed areas, and then overall exposing with an actinic radiation to cure the photosensitive layer in the unmasked areas. The remaining areas of the mask layer and the non-hardened portions of the photosensitive layer are then removed by one or more liquid development processes. Examples of flexographic articles having an ablatable mask layer are described in U.S. Pat. No. 5,262,275 to Fan, U.S. Pat. No. 5,705,310 to Van Zoeren, U.S. Pat. No. 5,719,009 to Fan, U.S. Pat. No. 6,020,108 to Goffing, et al., and U.S. Pat. No. 6,037,102 to Loerzer, et al.
While elements having a laser-ablatable mask layer allow direct imagewise exposure with a laser and do not require a separate masking device, the imaging time to create the mask is very long since the sensitivity to infrared radiation is low for the known integral mask systems. Sensitivity is generally not lower than about 1 j/cm2, and typically about 3 J/cm2 is required for laser-ablation imaging.
In recent years attempts have been made, such as reported in U.S. Pat. No. 6,521,390 to Leinenbach, et al., to improve the infrared sensitivity of an ablatable mask layer by using heat-combustible polymeric binders and specific aliphatic diesters. Although higher sensitivity and, as such, shorter exposure time may be achieved, this construction suffers from undesirable adhesion of the ablatable mask layer to a coversheet that must be removed before exposure; see U.S. Pat. No. 6,599,679 to Philipp, et al. at C1 and C2, Table 2.
Higher sensitivity is difficult with the integral-mask construction as the laser-ablatable layer must satisfy a number of widely varying quality criteria; see U.S. Pat. No. 6,599,679, col. 2, line 1-29. The use of a polyether-polyurethane binder in an ablatable layer is reported in U.S. Pat. No. 6,599,679, but the enhancement in imaging speed was modest (Examples 1-3 reported at Table 2; cf. Comparative Example C6).
Furthermore, the integral-mask approach for the production of flexographic printing plates requires the use of high-powered laser-equipped imagers specifically configured for imaging the flexographic articles, such as CYREL Digital Imager (CDI SPARK) manufactured by Esko-Graphics (Kennesaw, Ga.), and ThermoFlex by Creo (Burnaby, British Columbia). Because of the need for varying the thicknesses of a flexographic plates depending upon the specific printing application, more than one imager may be required with the integral-mask approach.
In contrast, conventional imaging apparatus for “computer-to-plate” lithographic applications (e.g., TRENDSETTER from Creo), and digital proofing applications (e.g., DESERTCAT 88 from ECRM) may be used in the present invention that use the film to make a mask image.